Over the past seven years, in collaboration with Think Brick Australia, researchers from the Centre for Energy at the University of Newcastle have been involved in a wide range of experimental and analytical activities studying the thermal performance of various walling systems commonly used in Australian housing. This collaboration between the Masonry Research Group in Civil engineering and researchers from Chemical Engineering has involved guarded hot box tests and the construction and extensive monitoring of the performance of four, full scale purpose built housing test modules incorporating typical walling systems - cavity brick, insulated brick veneer, insulated cavity brick and insulated lightweight construction. This paper is concerned with a critical examination of the wall thermal resistance (R value) and its impact on thermal performance. Twelve months of experimental results are presented and used to explore the difference in thermal behaviour of the modules incorporating the four walling types. It is shown that the wall thermal resistance is not the only factor influencing the thermal performance, indicating a potential deficiency in the current Australian building regulations which assume that the thermal resistance (R) value of the wall to be the principal design parameter influencing thermal performance.